On Fri, 1 Jan 2021 11:24:52 +0000, Martin Brown wrote:

You can't really prevent the roofing felt from being cold so you have to
get the humidity lower somehow.

Prevent moisture getting in or allow more fresh air to displace it.

+1

or combination of both.

Are the holes where cables penetrate the ceiling for light fittings
vapour proof or just a roughly cut hole with loads of space around
the cable? Particulary for fittings in rooms with high humidty,
kitchen, bath/shower rooms. Are any ceiling down lighters open at the
back? They ought to be fire proof anyway to slow the spread of fire
from the room to loft space.

--
Cheers
Dave.